The invention relates to a metal/plastic hybrid and also to a shaped body produced therefrom.
An electrical and/or electromagnetic and/or thermal conductivity is required for many applications of plastics in electronics and electrical engineering. There are today a large number of plastic compounds which cover a range of specific volume resistance from 1010 Ωcm to 10−1 Ωcm. A few special products, which contain carbon fibers as a filler for example, achieve approx. 2×10−2 Ωcm. Carbon black, carbon fibers, metal particles, metal fibers or intrinsically conducting polymers for example are used as electrically conducting fillers. However, no thermoplastic compounds are known thus far which have a specific volume resistance of less than 10−2 Ωcm and are capable of being processed in an injection molding process, for example.
In order to make an insulator such as plastic conducting, continuous conducting paths are created by way of electrically conductive fillers, in other words the conductive particles are ideally in contact with one another. It is known that the best way of realizing a conducting network in the plastic is to incorporate metal or carbon fibers. In this situation, the longer the fiber, the lower is the proportion by weight of fibers that is required for a particular conductivity. As the fiber length increases though, the processing also becomes more problematic because the viscosity of the compound increases significantly. Thus it is that compounds which are obtainable on the market having a steel fiber length of 10 mm can only be processed in the injection molding process up to a maximum proportion by weight of fibers of approx. 25-30%. When shorter fibers are used, compounds having higher proportions by weight of fibers can still be processed in the injection molding process but this does not result in any lowering of the specific volume resistance when compared with the long fiber. Similar characteristics are exhibited by thermoplastics filled with carbon fibers and metal particles. A further problem consists in the fact that, dependent on different coefficients of expansion, the fiber network in the filled thermoplastics stretches due to the effect of temperature and the conducting paths are interrupted.
Attempts are also made to incorporate only low melting-point metal (fusible alloys) in plastic, but only fill levels of 40-50% by weight are achieved as a result, with a specific volume resistance in the order of magnitude of 105 Ωcm. Higher fill levels are excluded on account of the poor compatibility and the large differences in density between the two components to be mixed.